Composite thread.



Jim 1956 H. c. DONALDSON, JR 2,731,788

COMPOSITE THREAD Filed Oct. 8, 1949 IN VEN TOR.

HARRY C. DONALDSON, JR.

BYOhM ATTORNEY United States Patent C) COMPOSITE THREAD Harry C. Donaldson, .l'r., Brunswick Township, Rensseiaer County, N. Y., assignor to Ciuett, Peabody & Cd, Erie, Troy, N. Y., a corporation of New York Application October 8, H49, Serial No. 129,245

1 Claim. (Ci. 57-446) ly laundered, to the fabrics so connected, and to the method of forming such a seam.

It has long been recognized that when abutting textile fabrics are united by stitching with the conventional or usual sewing thread, and especially stitching made by a sewing machine, even though the fabrics have been preshrunk, a subsequent laundering will result in further substantial shrinkage of the united fabrics. Stitch puckering in a laundered seam has also been a problem that many have sought to solve. Various efiiorts have been made to overcome the difficulty of scam shrinkage, because it was necessary, when forming garments, to make the garments somewhat oversize in order to allow for the seam shrinkage, notwithstanding that the fabric used had been previously pre-shrunk to approximately zero residual shrinkage. One attempt to solve this problem was to place sheet material over the fabrics to be united, stitch them all together and then tear out the superposed sheet material in order to leave slackness in the stitching. This has not been satisfactory because it is a slow and expensive manner of forming the seams.

Others have attempted to solve this problem by working on the theory that seam shrinkage in a fabric was caused by the stressing of the sewing thread during the mechanical sewing operation, and by the subsequent shrinkage of the thread in launderings in the same manner that a clothes line will shrink when wet and dried. Other efforts to compensate for this shrinkage have included the placing of fingers beneath the thread during the sewing operation, and then removing the fingers after the stitch was made, but these have not been entirely satisfactory for the reason that the full speed of the sewing machine could not be employed, and for other mechanical reasons. Various efforts have been made to prevent stitch puckering such as by the use of threads of different materials, but have been unsuccessful.

I have determined that although thread shrinkage does have some effect on seam shrinkage and stitch puckering, other factors have a more important influence thereon, one .factor being the type of fabric used. I have found that the fibers in the parts of the fabric yarns imprisoned or encircled by the loops of stitching thread swell considerably during the washing of the fabric, and the degree of swelling is dependent upon the kind of fiber in the fabrics. This swelling causes the loops of the sewing thread in the seam to draw together, pulling or compressing together the fibers or fabric so imprisoned in each loop. This causes the united fabrics to shrink and pucker along the seams. To verify the correctness of this observation, a number of fabrics were united in groups of a plurality of layers each, by stitching them together, but all of those in each group were made of the same kind of fibers, and in each group the fabrics were all stitched together with 2,731,788 Patented Jan. 24, 1956 the same kind of cotton sewing thread. The connected fabrics were then laundered to determine the seam shrink age.

If the shrinkage of the cotton thread alone was the cause of the seam shrinkage, one would expect to find the same shrinkage in each seam regardless of the character of the fibers of which the united fabrics were made, but the results indicated that the seam shrinkage varied considerably with the character of the fibers of which the fabrics were made. For example, when the fabrics were made of fibers which did not swell appreciably when wetted, the shrinkage was relatively small. Fabrics made of glass fibers when stitched together by this cotton sewing thread had only a very slight shrinkage and stitch puckering, whereas when the fabrics were made of cotton .fibers, seam shrinkage and puckering were quite substantial.

I have discovered that this scam shrinkage and stitch puckering can be substantially eliminated by using as a sewing or stitching thread that unites the fabrics, a composite sewing thread having a component that is soluble in a liquid in which the other component is relatively inert. More particularly I have discovered that such a thread may advantageously have one component which is soluble in the usual laundry washing solutions and another component which is insoluble or inert in such solutions. When a seam having such a composite thread in it is washed or laundered in the usual manner, the soluble component is removed and thus creates a slack or looseness in the other component that compensates for swelling of the fabric fibers without shrinkage or stitch puckering. In practice the composite thread may advantageously be formed by plying a strand or sewing thread of any usual or suitable sewing thread material with a strand or sewing thread that is soluble or disintegrable in the usual laundry washing solutions. The usual thread ply has a desired degree of twist with the soluble ply. For example, a thread of water soluble polyvinyl alcohol may be plied with a conventional sewing thread ply of any-suitable material, in which, the conventional sewing thread ply has a desired amount of twist with the ply of polyvinyl alcohol. This may be obtained by winding the conventional or insoluble ply spirally upon or intertwining it with the soluble thread, so that when the soluble thread or ply is subsequently removed after the seam has been formed, there will be no injury to the fabrics or the conventional sewing thread, and there will be created a predetermined degree of slackness in the residual thread at the exact time when it is needed to prevent puckering and shrinkage. This improved composite thread may be used to unite knitted as well as woven fabrics.

in the accompanying drawing, I have illustrated somewhat schematically the manner in which this invention may be applied in the formation of seams, and in this drawing:

Fig. 1 is a plan of several superposed layers of fabric connected together by this composite thread, and afterwards laundered to remove or disintegrate the core, a portion of the upper fabric layer being magnified in the .portion shown in the circle;

Fig. 2 is .a sectional elevation through the magnified portion of the connected fabric layers, the section being taken approximately along the line 2-2 of Fig. 1;

Fig. 3 is a sectional elevation similar to Fig. 2, but before the connected fabrics have been laundered so as to show the composite stitching thread on a magnified scale;

Fig. 4 is a magnified elevation of a short piece of one composite thread which may be employed in the stitching operation in accordance with this invention; and

Fig. 5 is a magnified elevation of a short length of another composite thread which may be employed in the stitching operation in accordance with this invention.

In the illustrated example of the invention, a plurality of superposed layers 1, 2 and 3 of textile fabric have been stitched together on a conventional sewing machine to form a seam, using the improved composite sewing thread 4 to unite the layers. This composite sewing thread is formed of at least two components 5 and 6, one, such as 5, being soluble or disintegrable in some liquid, and the other, such as 6, being relatively inert or insoluble in the same kind of liquid. The soluble and insoluble component fibers may be intermixed in a yarn or strand and the fibers twisted together to form the composite thread, or the soluble and insoluble fibers may be separately formed into threads, plies or strands, and then those various plies, strands or threads twisted together to form the composite thread. The latter is preferable, because when the soluble component is dissolved out it leaves a greater amount of excess thread length in each stitch, in the remaining or insoluble component of the thread. The soluble and insoluble plies or strands should be so twisted together in the thread, that when the soluble part is dissolved out, one will have in the insoluble component thread, just that excess of available length of insoluble thread which is desired or necessary in order to prevent shrinking of the fabric along the seam and to reduce stitch pucker. There are different ways in which this available slack in the insolvent thread may be obtained.

In Fig. 4, I have illustrated a thread or strand of the soluble fibers twisted together with a thread or strand of insoluble fibers, both threads being of the same length and twisted together, or intertwined, and neither ply or thread component being straight, but twined about the other. In such a case the amount of available slack desired is created by increasing or decreasing the number of turns per inch of the twist given to the plies of the composite thread. The soluble and insoluble plies or strands being of different materials, one is likely to have different elongation characteristics under tension than the other, so that when the composite thread is stretched in sewing, one ply may elongate more than the other, become nearly straight, and give the appearance of the other having an overfeed on it. When the tension is released one ply may recover further than the other and give the appearance of one ply having more turns per inch than the other, or in other words, some overfeed on the other.

As shown in Fig. 5, one ply or component may be wound somewhat spirally on a straight or nearly straight ply or strand as the plies are intertwined or twisted together, because of the fact that the components of the composite thread may be under some tension as they are twisted together, and one ply may elongate more than the other. it is important that the insoluble ply or strand have more or less a spiral path around the soluble ply or strand, in that the soluble ply or strand keeps a substantial amount of the insoluble fibers away from the fabric, so that when the seam is washed and the soluble component is dissolved out, this will create available slack in the insoluble plies or strands in sufficient amount to compensate for the swelling of the fabric fibers and for any shrinkage of the insoluble plies or threads that unite the fabric layers in the seam. The fibers forming the soluble component may be twisted together or plied, if desired, before they are in turn plied or intertwined with the insoluble component, and similarly, the insoluble component may be formed of twisted fibers forming one ply or strand. The insoluble component may, if desired, be formed of a plurality of small plies or strands of the insoluble fibers twisted. together or intertwined before being intertwined with the soluble component.

The amount of the excess of insoluble thread created by the dissolving out or disintegration of the soluble component which .may-for lack of a better termbe referred to as overfeed, may be varied to a considerable 4 extent by varying the number of turns per inch in the twist given the composite thread as the plies are combined, of by varying the number of turns per inch given the fibers or strand forming the composite thread where the soluble and insoluble fibers are blended or combined before being twisted to form a common ply or thread.

The preferred manner of combining the soluble and insoluble plies is to separately form plies, strands or threads of each, then twist them together in a suitable twister, such as is commonly found in textile mills. Such twisters have the spindle or bobbin on which the composite thread is wound, rotated at a fixed rate. By varying the rate of feed of the plies or strands to the traveller through which the combined strands travel on the way to the bobbin, one may vary the number of turns per inch of twist given to the combined plies. One selects the number of turns per inch to be given to the combined plies or strands in order to determine the amount of excess thread of the insoluble ply that will be available after the soluble component has been dissolved out. The amount of desired slack to be created in the seam during laundering will depend somewhat on the character of the fibers from which the fabrics are made. When the fabrics are made of fibers that have a tendency to swell substantially when wet, it is advisable to use a composite thread which will release a greater amount of insoluble thread during laundering than when the fibers of the fabric have a lesser tendency to swell.

For preshrunk cotton broadcloth fabrics connected by needle and bobbin, composite threads employing a conventional cotton sewing thread as a permanent component thereof, the excess length of the insoluble component that will be released by the dissolving out of the soluble component should preferably be at least about six percent (6%). When the composite thread is used only as one of the uniting threads, such as the bobbin thread, and a conventional thread is used as the other uniting thread, the excess length of'the insoluble component that will be released should preferably be at least about twelve (12%) percent.

It is not necessary that the needle thread and the bobbin thread, sometimes known as the top and bottom threads, both have the same amount of twist or available slack, but the total available slack provided by the needle and bobbin threads together, when the'soluble component is removed, should be suificient to prevent seam shrinkage or stitch puckeriug. Since the amount of slack required varies with the character of the fibers of the fabric that are united, this will be subject to some variation. If too much available slack or overfeed is provided, then after the fabric is washed or treated to remove the soluble component, the remaining slack in the stitch may be unsightly. If the composite thread is used only in the bottom or bobbin thread, and sewing cotton thread is used as the needle thread, it may be advisable to use as much as about 28% ormore excess thread that will be made available by the removal of the soluble component.

The soluble component 5 should be formed of a material which may be easily removed from the connected fabrics, such as a material which is either soluble or will disintegrate in a liquid in which the fibers of the fabrics and the conventional sewing thread are inert or substantially insoluble. It is desirable that the soluble component be one which is removed in the normal laundering or washing of the fabrics united by such a seam, in order to make unnecessary any special treatment of the connected fabrics. There is no necessity for the creation of the slack in the thread, nor would it be desirable, until the garment or united fabrics are washed. For that reason the soluble component should, preferably, be one that is soluble in water or in any of the usual laundry washing solutions, Excellent results have been obtained when the soluble components are made of water soluble,

polyvinyl alcohol as that material is available in staple fiber and filament form and is readily soluble in and quickly disintegrates in water.

Another material which can be used as a soluble component is alginate rayon, which is soluble in weak alkaline solutions, such as the weak caustic solutions provided in some detergents and soap solutions. One may also employ as the soluble component, threads or strands of various other water soluble materials that are capable of being formed into fibers or filaments, among which may be mentioned, for example, carboxymethylcellulose, polymethacrylic acid and polyacrylic acid. One may also use other materials as the soluble component, such as, for example, cellulose acetate. As the insoluble component, one may use any of the usual fibrous materials that are suitable for the manufacture of sewing threads, among which may be mentioned fibers or threads of nylon, Orlon, fiber V, cotton, linen, silk, rayon, wool, cellulose acetate, ramie and jute.

The removal of the soluble component or its disintegration in this manner provides a uniformly distributed slack in the conventional sewing thread used in making the seam, and therefore, the swelling of the fibers in the conventional sewing thread, will pick up and distribute this slack so that the remaining conventional thread will lie along the connected layers without slack and without material tension. The swelling of the fibers will merely take up the created slack and will not cause a pulling together of the yarns of which the fabrics are made. Consequently, the tightening of the sewing threads will not cause the fabrics to shrink along the scams, or cause stitch pucker.

When the soluble thread or component is made of alginate rayon, the subsequent washing of the fabricsunited by this seam in most washing solutions will usually result in a disintegration or dissolving of the alginate rayon, for the reason that most washing solutions are slightly alkaline. The united fabrics may, of course, be immersed in a specially prepared weak alkaline solution if one does not expect to use a laundry operation employing a mildly alkaline detergent.

When the soluble thread or component is formed of cellulose acetate or some other material which is not readily soluble or disintegrable in the usual laundry bath, it is necessary to soak the united fabrics in a solvent for that material, such as acetone for cellulose acetate, to dissolve out or disintegrate the soluble component after the seam has been formed.

in the practice of this discovery a composite :thread is made up, as shown in Figs. 4 and 5, of a soluble component 5 incorporated in or intertwined with an insoluble component 6. Each component of itself may be a plied thread or strand if desired, and these plied components then intertwined or plied together, with an available excess of the insoluble component when the soluble com ponent is removed. The composite thread so obtained may be employed as a sewing thread, and any of the suitable binders or lubricants may be incorporated in or applied to this composite thread. This composite thread may be used in a sewing machine of standard make to unite the fabric layers. Some of it may be used as the bobbin or shuttle thread to form the bottom thread of the seam, and some may be substituted for the usual sewing thread, that passes through the usual tension device, needle eye, and the usual thread feeding and guiding mechanism. Sewing is performed in the usual manner so as to stitch together or unite the superposed fabric layers 1, 2 and 3, as shown in Fig. 3. By using the composite thread for both the needle and bobbin threads that forms a seam, it is not necessary to use as much twist per unit length, or overfeed of the insoluble or inert strands or plies on the soluble component, as when the composite thread is used only in one of the sewing threads. it is also not necessary that there always be the same amount of available slack or thread excess of the inert or insol- 6 uble component in both needle and bobbin threads, but the available excess of the inert or insoluble thread or component in one or both threads of the seam should total that required to give the desired slackness in the threads of the seam after the united fabrics are washed or laundered.

In making garments, the various superposed layers are united by stitching seams as part of the operation of making the garment, and when this composite thread is used as one or both of the threads that form these seams, one may have normally appearing seams, yet when the garment so made is washed, the slackness created by removing the soluble component prevents shrinkage and stitch puckering along the seams. In collars "and shirt neckbands there are often a plurality of closely arranged rows of stitching which cause a serious problem of seam shrinkage, and stitch pucker, but by using this composite thread as one or both of the threads that form each seam, the finished garment will have the usual, visual appearance, and one would not know from casual inspection that the seams were formed by anything but a conventional sewing thread. After the garment has been washed and the soluble component disintegrated or removed, the sewing thread in the seam still has the usual appearance.

It is known that it is not necessary to use as large a thread as is conventionally used in sewing seams, in order to have the necessary seam strength, but the larger thread is commonly used because of the fact that a smaller thread is likely to break frequently during the sewing operation due to the force to which the thread is sub jected. in accordance with this discovery, the composite thread can use as its soluble component or ply, a smaller thread than has been heretofore necessary, and yet have adequate seam strength.

As one specific example, three layers of cotton broadcloth fabric that had been previously shrunk so as to have less than 1% residual shrinkage, were united on a conventional sewing machine by a seam using, in one instance, a conventional cotton sewing thread and in the other instance a special composite thread employing a two hundred denier polyvinyl alcohol ply thread upon which was wound a conventional 70/2 cord cotton sewing thread with a six (6%) percent overfeed of this conventional cotton sewing thread on the polyvinyl alcohol ply. Samples made up in this manner were then subjected to three standard cotton wash tests commonly employed for determining shrinkage of cotton fabrics, approved in Department of Commerce Government bulletins entitled Federal Specifications and which are known as CCC-T-l91a cotton wash tests.

The result in seam shrinkage is tabulated as follows, the seam shrinkage being measured for each washing:

As another specific example, various types of composite threads were constructed and used to sew together three-ply seams of cotton woven fabric that had been previously shrunk so as to have less than 1% residual shrinkage.

The threads used are identified as follows:

V-l5 sewing thread, Premier 70 denier-fiber V yarn, approximately twenty-four (24) turns per inch, S-twist.

70/ 2 cotton sewing thread, Pacific.

/2 cotton sewing thread, American.

Polyvinyl alcohol thread.

The seams so formed are identified by letters as follows:

Seam A--forrned of composite thread of fiber V-lS and polyvinyl alcohol fibers, ten turns per inch, 8- twist, used in both the needle and bobbin threads.

Seam Bformed of composite needle thread of fiber V-lS and polyvinyl alcohol plies, twenty (20) turns per inch, S-twist, and a composite: bobbin thread formed of fiber V and polyvinyl alcohol threads, with ten (10) turns per inch and S-twist.

Seam Chad a composite needle thread made from two ends of 70 denier fiber V yarn and polyvinyl alcohol yarn, twenty-two (22) turns per inch, Z-twist, and a composite bobbin thread formed of fiber Vl5 and polyvinyl alcohol threads plied together, with ten (10) turns per inch, S-twist.

Seam D-had both needle and bobbin threads each formed of two plied ends of 7G denier thread of plied fiber V yarn and polyvinyl alcohol yarn, twenty-two (22) turns per inch and Z-twist.

Seam Ehad both needle and bobbin threads formed of plied threads of fiber V-l5 thread and polyvinyl alcohol thread, twenty turns per inch, S-twist.

Seam Fis a regular seam having as the top or needle thread conventional 70/2 cotton sewing thread, and a bobbin thread of conventional 80/2 cotton sewing thread.

All but the regular seam were given a hand wash, then dried and measured, then all seams were given the white cotton commercial wash test, and then dried and measured. A specimen of each composite thread was also marked at eighteen inch lengths, while under 100 gm tension, and then washed in skein form to remove the soluble, polyvinyl alcohol component, and then the thread was measured under the same tension to determine the excess thread available. The results of these thread measurements were as follows:

Flfllxcess Turns S or Z enga- Cmposlie Thread Per Inch Twist tion,

percent 70/2 cotton and polyvinyl alcohol 20 S 14. 6 140/2 cotton and polyvinyl alcohol 20 S 9. 7 V-l5 and polyvinyl alcohol 10 S 4. 6 Do 20 S 9. 7 Two ends of 70 denier V and polyvinyl alcohol 20 Z 9. 7

The shrinkage in the washed seams is indicated as follows:

slPerfient Excess Thread llllIl 86- Senni {fi s White Fa fbric Commercial Needle, Bobbin,

Wash percent percent 0. l 4. 6 4. 6 0. 2+ 9. 7 4. 6 ll. 5 5. 5 4. 6 0. 2+ 5. 5 5. 5 0. 4+ 9. 7 9. 7 2. 7 0 0 (-l-denotcs a gain.)

As a further example, tests were made of a three-ply scam in the same kind of cotton broadcloth, using a composite thread only as the bobbin thread of the seam, and using a conventional cotton sewing thread as the needle or top thread. This composite thread used as the bottom thread was formed of the conventional cotton thread 140/2, plied with 'water soluble polyvinyl alcohol thread having ten turns per inch, and S-twist. The cotton thread and the polyvinyl alcohol threads were plied together to have thirty-two turns per inch of S-twist, and with an available excess of cotton thread of approximately 28%. The top or needle thread used in forming the seam was 70/2 conventional cotton sewing thread. The complete seam was then subjected to the standard cotton wash test, known in the trade as CCC-T-l9la, after which the shrinkage was measured and found to be 0.1% in the seam, and substantially no stitch pucker was present. To compare this with the standard seam formed of all-cottonsewing thread, a seam was formed of three plies of cotton broadcloth of the same type as given above for the other examples, using as the top or needle thread 70/2 cotton sewing thread, and as the bobbin or bottom sewing thread 2 conventional cotton sewing thread. That seam was also at the same time subjected to the same standard cotton wash test and its shrinkage was found to be 5.3%. There was considerable stitch pucker along the seam. This indicates that shrinkage and stitch pucker may be substantially eliminated by using a composite thread as the bobbin thread, and a conventional sewing thread as the needle thread.

As a further example, threads of materials other than cotton were plied with a water soluble component such as polyvinyl alcohol. In this example, the letters PVA are used as an abbreviation of water soluble, polyvinyl alcohol. A series of composite threads were made up as follows:

I also obtained five (5) conventional sewing threads of the following materials: 70/ 2 cotton; Neophil nylon; Portisan; Orlon; fiber V.

The fabric used was a woven cotton fabric that had previously been shrunk so as to have a residual shrinkage less than 1%. Three layers of such fabric were then sewed to form seams, a separate seam being formed with each of the above composite threads and also with each of the above conventional sewing threads. The seams were marked at eighteen inch (18") lengths, and the seamed fabrics were subjected to the standard cotton wash testCCC-T-l9la, which last one hour, after which the specimens were all dried at room temperature and the shrinkage measured. The shrinkage results were as follows:

Scam Shrinkage Inch Perccn tagc 0. 00 9i 6 0. 69 910 0. 69 at o l. 04 3 15 0. 69 7 s 2. 43

Va 3. -17 this 2. 7s i6 2. 78 i o 2. 78

It is, therefore, obvious that composite threads may be used that have any of the conventional sewing threads as one component thereof, and a soluble ply as another component, and all will satisfactorily eliminate seam shrinkage. It was also found that when using each of the composite threads of this example, substantially no stitch packer was created after laundering, but where the conventional sewing threads of this example and having no soluble component were used, there was substantial stitch pucker along the seams.

The soluble component may be in either filament or staple fiber form, and each may be plied or unplied as desired. The contraction of the strands of soluble and insoluble components, as they are twisted together, provides available slackness when the soluble component is removed and the insoluble component can straighten out. The greater the twist given to the component plies or strands as they are intertwined, the greater will be the available elongation of the insoluble ply or strand when the soluble component is removed.

It will be understood that fabrics of any material may be united by seams using this improved composite thread as the needle thread, the bobbin thread, or both. For example, not only cotton fabrics but those made from any of the other fibers, including those of cellulose acetate, nylon, Orlon, fiber V, linen, silk, rayon, wool, ramie and jute may be united by this improved composite thread, with substantial elimination of seam shrinkage and stitch pucker. In some fabrics, such as those made of nylon, there is sometimes a small stitch pucker and seam contraction caused by the sewing operation, and in such cases it is desirable to increase the twist, or the available slack in the insoluble component, of the composite thread so that there will be a slight gain in the seam after laundering. Thus as the thread is relaxed or elongated in laundering a scam, the stress in the thread that caused the original stitch pucker and seam contraction, from the act of sewing the fabrics together, is relaxed so that the fabric along the seam resumes its normal appearance. As an example, three layers of 100% nylon woven fabric were stitched together, using as both needle and bobbin threads, :1 composite thread formed by plying 70/2 conventional cotton sewing thread with a water soluble, polyvinyl alcohol thread, having ten turns per inch and S-twist in the composite thread. There were fourteen (14) stitches per inch in the seam. When the nylon fabrics so connected were given a hand wash at a temperature of between 100 F. and 110 F. and allowed to dry in air at room temperature, the shrinkage in the seam was found 10 to be 1.73% gain and an elimination of substantially all of the stitch pucker.

The results illustrate that seam shrinkage and stitch pucker can be substantially eliminated by the use of this composite thread as either the bobbin or needle thread, or both. The sewing machines do not need modification, and may be operated at their usual speed and in the usual manner.

It will be understood that various changes in the details and materials, which have been herein described and illustrated in order to explain the nature of the discovery, may be made by those skilled in the art within the principle and scope of the discovery, as expressed in the appended claim.

I claim:

A composite sewing thread for use in stitching together superposed layers of textile fabrics to form a seam having minimum shrinkage and stitch pucker, which comprises a multiple ply, relatively highly twisted, sewing thread, one ply of which is of water soluble polyvinyl alcohol, and another ply of which is substantially water-insoluble and in itself a complete sewing thread.

References Cited in the file of this patent UNITED STATES PATENTS 132,926 Sheflield Nov. 12, 1872 908,771 Hendry Jan. 5, 1909 1,987,453 Thomas et a1. Jan. 8, 1935 2,189,067 Hlavaty Feb. 6, 1940 2,211,850 Dreyfus Aug. 20, 1940 2,251,962 Sommaripa Aug. 12, 1941 2,331,955 Beebe et al Oct. 19, 1943 2,332,020 Simpson Oct. 19, 1943 2,332,738 Meade Oct. 26, 1943 2,435,543 Johnson et al Feb. 3, 1948 2,531,839 Camp Nov. 28, 1950 2,714,758 Woodson Aug. 9, 1955 

